Semiconductor device including antifuse element

ABSTRACT

An element isolation region exists at a side opposite to a diffusion layer region as seen from a channel region, without another electrode to which the same potential as one applied to the diffusion layer region is applied interposed between the channel region and the element isolation region. The electric field applied to the gate insulating film is not uniform and the magnitude of the electric field is increased when approaching closer to the diffusion layer region. Therefore, breakdown is likely to occur at parts closer to the diffusion layer region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. application Ser. No. 12/196,325 filed Aug. 22, 2008 which claims priority from Japanese Patent Application No. 2007-217765 filed Aug. 24, 2007, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an antifuse element and a semiconductor device including the same, and, more particularly relates to an antifuse element that can be changed from an electrically isolated state to an electrically conductive state by dielectric breakdown and a semiconductor device including the same.

2. Description of the Related Art

In semiconductor devices including a DRAM (Dynamic Random Access Memory), defective cells that do not operate properly are replaced with redundancy cells to relieve defective addresses. Usually, fuse elements are utilized to store the defective addresses. Laser beams are irradiated to the fuse elements so as to disconnect them irreversibly, so that the defective addresses are stored. The usual fuse elements can store information in a nonvolatile manner by changed from the conductive state to the isolated state.

Meanwhile, antifuse elements have attracted attention in recent years (see U.S. Pat. Nos. 6,902,958 and 6,700,176, and U.S. Patent Application Publication No. 2005/0258482). The antifuse elements store information, as opposed to the usual fuse elements, by changed from the isolated state to the conductive state. The configuration of the antifuse elements is almost the same as that of depletion MOS transistors. When the gate insulating film is subjected to breakdown by a high voltage applied between the gate electrode and the electrode common to the source and drain, the antifuse element is changed from the isolated state to the conductive state.

Because the antifuse element has the same configuration as the depletion MOS transistor, its occupied area is smaller than the usual fuse element and the passivation film is not broken by the laser irradiation.

However, the antifuse element has a problem of a large variation in resistance in the conductive state. Reasons why the resistance is varied in the conductive state are explained below.

FIG. 11 is a schematic diagram of a configuration of a conventional antifuse element.

As shown in FIG. 11, a generally used antifuse element includes a gate electrode 12, a source region 14, and a drain region 16. The source region 14 and the drain region 16 are shorted by the wirings. In the initial state, the gate electrode 12 is isolated from a channel region 20 by a gate insulating film 18. The gate electrode 12 is thus isolated from the source region 14 and the drain region 16. When a breakdown region 18 a is formed in the gate insulating film 18 by applying a high voltage to the gate electrode 12, the gate electrode 12, the source region 14, and the drain region 16 are short-circuited via the depletion channel region 20.

Thus, by detecting whether current flows between a terminal D connected to the gate electrode 12 and a terminal E connected to the source region 14 and the drain region 16, whether the breakdown region 18 a is formed in the gate insulating film 18 is determined.

FIG. 12 is an equivalent circuit diagram of the antifuse element in the breakdown state.

As shown in FIG. 12, if the antifuse element is subjected to breakdown, a resistance component Rg for the gate electrode 12 and the breakdown region 18 a is connected to a parallel circuit of a channel resistance component Rs on the source region 14 side and a channel resistance component Rd on the drain region 16 side between the terminals D and E. The resistance components Rs and Rd vary depending on the position of the breakdown region 18 a formed. The position of the breakdown region 18 a formed depends on a predetermined probability distribution. The breakdown region 18 a can be formed in the vicinity of the source region 14 or the drain region 16, or can be formed at the substantial intermediate position between the source region 14 and the drain region 16.

That is, the source region 14 and the drain region 16 are short circuited by the depletion channel region 20 and by the upper wiring. When voltage is applied to the gate electrode 12, substantially uniform electric field is applied to the gate insulating film 18. Therefore, if the thickness and quality of the gate insulating film 18 are uniform, breakdown can occur equally at any part of the film. It is thus impossible to predict the forming position of the breakdown region 18 a.

When the breakdown region 18 a is formed in the vicinity of the source region 14 or the drain region 16, one of the resistance components Rs and Rd is reduced significantly. The resistance between the terminals D and E is thus relatively small. When the breakdown region 18 a is formed at the substantial intermediate position between the source region 14 and the drain region 16, the resistance components Rs and Rd are increased, resulting in relatively large resistance between the terminals D and E.

When Rs=Rd, that is, when the breakdown region 18 a is formed at the intermediate position, the resistance Rde between the terminals D and E is given by the following formula.

Rde=Rg+Rs·Rd/(Rs+Rd)=Rg+Rd/2

In contrast, when Rs>>Rd, that is, when the breakdown region 18 a is formed at either of the ends (e.g., in the vicinity of the drain region 16), Rd≈0. The resistance Rde between the terminals D and E is given by the following formula.

Rde=Rg+Rs·Rd/(Rs+Rd)≈Rg

A normal sheet resistance is a hundred and several tens Ω/□ on a gate resistance layer and a few KΩ/□ to a several hundred MΩ/□ on a depletion channel resistive layer. The resistance Rde depends substantially on the depletion channel resistive layer.

Even if the antifuse element is subjected to breakdown in the substantially same voltage conditions, the forming position of the breakdown region 18 a is unpredictable. As a result, the resistance between the terminals D and E is inevitably varied greatly. Such a variation makes it difficult for thresholds to be set when it is determined whether the breakdown region 18 a is formed. Sometimes that may cause wrong determination. The resistance between the terminals D and E may be relatively large even after breakdown. The detection sensitivity needs to be set high to some extent. The time required for determination is extended, which prevents high speed operation of semiconductor devices.

SUMMARY

The present invention seeks to solve one or more of the above problems, or to improve upon those problems at least in part.

In one embodiment, there is provided a semiconductor device having an antifuse element, the antifuse element comprising: an upper electrode; a lower electrode; an insulating film located between the upper electrode and the lower electrode; an extraction electrode located adjacent to the lower electrode; and an element isolation region provided at an opposite side of the extraction electrode as seen from the lower electrode without intervention of another electrode to which a same potential applied to the extraction electrode is applied, wherein the upper electrode and the extraction electrode can be electrically connected via the lower electrode by forming a breakdown region in the insulating film.

It is preferable that a part of the upper electrode is formed on the element isolation region. It is preferable that the predetermined end of the upper electrode substantially coincides with a boundary between the lower electrode and the extraction electrode as seen from a planar view and is formed in a non-linear configuration.

“The non-linear configuration” includes any configurations that realize longer distance of a unit interval than a linear distance including a curved configuration and a zigzag configuration. Configurations that realize the distance of the unit interval longer than the linear distance by 50% or more are effectively desirable. According to the present invention, the longer distance of the unit interval is preferable. That is, it is preferable that the predetermined end of the upper electrode is extended. The zigzag configuration is thus preferably used.

A semiconductor device according to the present invention preferably includes the antifuse element, a write circuit for causing breakdown of the insulating film by applying a high voltage to the upper electrode, and a readout circuit for detecting resistance between the upper electrode and the extraction electrode.

According to the present invention, the electric field applied to the insulating film is not uniform and the intensity of the electric field becomes higher when approaching closer to the extraction electrode. Breakdown is thus likely to occur at parts closer to the extraction electrode, and therefore variation in resistance after breakdown is suppressed and the resistance after breakdown can be reduced.

With the antifuse element according to the present invention, when determining whether the antifuse element is subjected to breakdown, the time required for the determination is reduced without wrong determination. The antifuse element is applied to circuits requiring high speed operations.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of this invention will become more apparent by reference to the following detailed description of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1A shows a schematic plan view of an antifuse element according to a first embodiment of the present invention;

FIG. 1B shows a schematic cross-sectional view along the line A-A in FIG. 1A;

FIG. 2 is a circuit diagram showing a state that a write circuit and read circuit are connected to the antifuse element shown in FIGS. 1A and 1B;

FIG. 3A shows a schematic cross-sectional view of the antifuse element in the breakdown state;

FIG. 3B is an equivalent circuit diagram of FIG. 3A;

FIG. 4A shows a schematic plan view of an antifuse element according to a modified embodiment of the present invention;

FIG. 4B shows a schematic cross-sectional view along the line A-A in FIG. 4A;

FIG. 5 is a schematic plan view of an example that a plurality of the antifuse elements are arranged in an array;

FIG. 6A shows a schematic plan view of an antifuse element according to a second embodiment of the present invention;

FIG. 6B shows a schematic cross-sectional view along the line B-B in FIG. 6A;

FIG. 7A shows a schematic plan view of an antifuse element according to a third embodiment of the present invention;

FIG. 7B shows a schematic cross-sectional view along the line C-C in FIG. 7A;

FIG. 8A shows a schematic plan view of an antifuse element according to a fourth embodiment of the present invention;

FIG. 8B shows a schematic cross-sectional view along the line F-F in FIG. 8A;

FIG. 9 shows a schematic plan view of an antifuse element according to a fifth embodiment of the present invention;

FIGS. 10A to 10D are variations of the configuration of the gate electrode;

FIG. 11 is a schematic diagram of a configuration of a conventional antifuse element; and

FIG. 12 is an equivalent circuit diagram of the antifuse element shown in FIG. 11 in the breakdown state.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be explained in detail with reference to the drawings.

FIGS. 1A and 1B show a configuration of an antifuse element 100 according to a first embodiment of the present invention, where FIG. 1A is a schematic plan view, and FIG. 1B is a schematic cross-sectional view along the line A-A in FIG. 1A. A part of components including upper wirings is omitted in FIG. 1A for clarity of illustration.

As shown in FIGS. 1A and 1B, while the antifuse element 100 of the first embodiment has, as conventional antifuse elements, a similar configuration to that of a depletion MOS transistor, it is different from the conventional antifuse elements in that one of a source region and a drain region is removed. Detailed explanations are given below.

The antifuse element 100 according to the first embodiment includes a gate electrode 110 as an upper electrode, a depletion channel region 120 as a lower electrode, a gate insulating film 130 located between the gate electrode 110 and the channel region 120, and a diffusion layer region 122 as an extraction electrode. In spite of the channel region 120 forming a PN junction with the diffusion layer region 122, they are in the conductive state because the channel region 120 is of the depletion type.

As shown in FIG. 1A, the end 111 of the gate electrode 110 on the diffusion layer region 122 side coincides with a boundary between the channel region 120 and the diffusion layer region 122 as can be seen from a planar view. Such a configuration is obtained by implanting ions in an active region 102 using the gate electrode 110 as a mask. Although not particularly restricted, other ends 112 and 113 of the gate electrode 110 coincide substantially with the periphery of the active region 102.

Only the channel region 120 and the diffusion layer region 122 are provided in the active region 102. Unlike normal antifuse elements, paired two diffusion layer regions do not exist. That is, one of the source region and drain region is removed.

As seen from a planar view, the active region 102 is surrounded by an element isolation region 104 which is surrounded by a contact region 106. The contact region 106 is surrounded by an element isolation region 108. As shown in FIG. 1B, the element isolation region 104 is provided within a P-well region 103 so as to be separated surely from other elements (not shown) formed in an N-type substrate 101. Potential is supplied from the ring-shaped contact region 106 via an upper wiring 140 and a contact 150 to the P-well region 103.

Potential is supplied to the gate electrode 110 via an upper wiring 161 and a contact 162. The upper wiring 161 is connected via a contact 151 to another upper wiring 141. Potential is supplied to the diffusion layer region 122 via an upper wiring 142 and a contact 152.

The contact 162 connecting the gate electrode 110 to the upper wiring 161 is placed immediately above the channel region 120. According to usual MOS transistors, a gate electrode includes a contact region extended on an element isolation region. A contact is usually formed on the contact region. If the contact is formed immediately above the channel region 120, transistor characteristics may be changed by stresses generated at the time of forming the contact. The function of the antifuse element may not be affected greatly by the changes in characteristics. The contact 162 is thus placed immediately above the channel region 120 in the first embodiment.

FIG. 2 is a circuit diagram showing a state that a write circuit and read circuit are connected to the antifuse element 100 according to the first embodiment.

As shown in FIG. 2, a write circuit 180 is configured by a switch connected between the upper wiring 141 which leads to the gate electrode 110 and a write voltage Vpp. A read circuit 190 is configured by a switch 191 connected between the upper wiring 141 and a read voltage Vdd and a comparator 192 connected to the upper wiring 142 which leads to the diffusion layer region 122.

In the initial state of the antifuse element 100, the gate electrode 110 is isolated from the channel region 120 by the gate insulating film 130. The resistance between the upper wirings 141 and 142 is thus substantially infinity. Current does not flow between the upper wirings 141 and 142. Even if the switch 191 shown in FIG. 2 is turned on, the potential of the upper wiring 142 changes little. In such a state, outputs from the comparator 192 are at a low level. It is detected that the antifuse element 100 is not subjected to breakdown.

When the write circuit 180 is turned on, a high voltage is applied to the gate electrode 110 so that the gate insulating film 130 is subjected to dielectric breakdown. The gate electrode 110 is thus connected to the channel region 120. Because the channel region 120 is of the depletion type, the gate electrode 110 is electrically connected to the diffusion layer region 122 via the channel region 120 when the gate insulating film 130 is subjected to breakdown. The resistance between the upper wirings 141 and 142 is reduced.

When the switch 191 shown in FIG. 2 is turned on, the potential of the upper wiring 142 is increased and outputs from the comparator 192 are at a high level. It is detected that the antifuse element 100 is subjected to breakdown.

When the write circuit 180 is turned on to apply high voltage between the gate electrode 110 and the channel region 120, the electric field applied to the gate insulating film 130 becomes higher when approaching closer to the diffusion layer region 122. This is because, unlike popular antifuse elements, two diffusion layer regions (source region and drain region) do not exist on the sides of the channel region. Instead, only one diffusion layer region exists on one side (on the left side in FIG. 1). As a result, a breakdown region is likely to be formed at parts of the gate insulating film 130 closer to the diffusion layer region 122. For example, when the breakdown region is formed in the vicinity of the end 111 of the gate electrode 110, the distance of the current path through the channel region 120 is substantially zero.

FIGS. 3A and 3B show the antifuse element 100 in the breakdown state, where FIG. 3A is a schematic cross-sectional view, and FIG. 3B is an equivalent circuit diagram.

As shown in FIG. 3A, when a high voltage is applied to the gate electrode 110, a breakdown region 130 a is formed in the vicinity of the diffusion layer region 122. The resistance Rde between the upper wirings 141 and 142 is defined, as shown in FIG. 3B, as the sum of the resistance component Rg for the gate electrode 110 and the breakdown region 130 a and the channel resistance component Rs. Because the breakdown region 130 a is formed in the vicinity of the end 111 of the gate electrode 110, the channel resistance component Rs becomes much smaller than conventional cases.

According to the antifuse element 100 of the present embodiment, one of the source region and drain region is removed. Therefore, the electric field applied between the gate electrode 110 and the channel region 120 during breakdown is biased, and breakdown is likely to occur at the end 111. As a result, a smaller variation in resistance after breakdown can be realized. A threshold Vref inputted to the comparator 192 is easily set and wrong determination is thus avoided. Reduced resistance after breakdown allows for determination in a short time.

Further, because the source region or drain region is removed, the area occupied by the antifuse element 100 is reduced. If breakdown occurs at the removed side (on the right side in FIG. 1), the resistance after breakdown is increased. While breakdown hardly occurs at the removed side, as described above, the electric field applied to the gate insulating film 130 becomes higher when approaching closer to the diffusion layer region 122 (the electric field becomes lower when coming away from the diffusion layer region 122).

According to the present invention, however, either the source region or the drain region does not need to be removed. As shown in FIG. 4B, which is a schematic cross-sectional view, another unused diffusion layer region 124 can be provided on a side opposite to the diffusion layer region 122, as seen from the gate electrode 110. Even if the diffusion layer region 124 is provided, it does not need to be connected to the upper wirings, and therefore the size of the diffusion layer region 124 does not need to be so large that contacts can be formed therein. If the element isolation region 104 exists at the side opposite to the side of the diffusion layer region 122 as seen from the of the channel region 120, without another diffusion layer region to which the same potential as one applied to the diffusion layer region 122 interposed between the channel region 120 and the element isolation region 104, the same effects as those of the antifuse element 100 shown in FIG. 1 can be obtained.

The contact 162 connecting the gate electrode 110 to the upper wiring 161 is placed immediately above the channel region 120 in the first embodiment. The contact region does not need to be formed separately, resulting in even reduced occupied area.

FIG. 5 is a schematic plan view of an example that a plurality of the antifuse elements 100 are arranged in an array.

As shown in FIG. 5, when a plurality of the antifuse elements 100 are arranged in an array, the ring-shaped contact region 106 does not need to be provided for each of the antifuse elements. The plurality of the antifuse elements 100 are surrounded by the single contact region 106. Although the antifuse elements 100 are separated from each other by the element isolation region from a planar point of view, such separation is sufficient for the antifuse elements 100. The total occupied area is reduced as compared to the case of providing the contact region 106 for each of the antifuse elements 100.

The antifuse element is a two-terminal element unlike conventional antifuse elements which are three-terminal elements. As shown in FIG. 5, an upper wiring 171 extending to the right side is connected to the gate electrode 110, while an upper wiring 172 extending to the left side to the diffusion layer region 122, resulting in a simplified layout.

FIGS. 6A and 6B show a configuration of an antifuse element 200 according to a second embodiment of the present invention, where FIG. 6A is a schematic plan view, and FIG. 6B is a schematic cross-sectional view along the line B-B shown in FIG. 6A. A part of components including upper wirings is omitted in FIG. 6A for clarity of illustration.

According to the antifuse element 200 according to the second embodiment, the length L of the channel region 120 is reduced greatly and the end 112 of the gate electrode 110 is placed above the element isolation region 104. Because the anifuse element 200 is the same as the antifuse element 100 shown in FIG. 1 in other respects, like reference numerals are denoted to like components and explanations thereof will be omitted.

Because most part of the gate insulating film 130 which does not expect breakdown is placed on the element isolation region 104 in the second embodiment, breakdown does not occur at this part. That is, breakdown is much likely to occur at the end 111. Even if breakdown occurs not at the ends but at other parts, the resistance of the channel region 120 is reduced sufficiently because of its reduced length.

Accordingly, variations in resistance after breakdown are further suppressed and the resistance after breakdown is further reduced. Further, because the active region 102 is reduced, the area the antifuse element 200 occupies is reduced correspondingly.

Normally, the part of the gate electrode 110 placed on the element isolation region 104 is not necessary. If the part is removed, however, the gate electrode 110 becomes so thin that it may be peeled away during patterning and the contact 162 is difficult to be formed. As shown in FIGS. 6A and 6B, it is thus preferable to form the gate electrode 110 above the element isolation region 104.

FIGS. 7A and 7B show a configuration of an antifuse element 300 according to a third embodiment of the present invention, where FIG. 7A is a schematic plan view, and FIG. 7B is a schematic cross-sectional view along the line C-C shown in FIG. 7A. A part of components including upper wirings is omitted in FIG. 7A for clarity of illustration.

According to the antifuse element 300 of the third embodiment, an end 111 of the gate electrode 110 is formed in a zigzag configuration in plan view. Because the anifuse element 300 is the same as the antifuse element 100 shown in FIG. 1 in other respects, like reference numerals are denoted to like components and explanations thereof will be omitted.

According to the researches of the present inventor, it has been found that breakdown is likely to occur at the ends of the gate insulating film as compared to the central part. This is because the gate insulating film is not perfectly homogenous, but inhomogeneous to some extent and breakdown thus occurs at parts with the lowest withstand voltage. The parts with low withstand voltage tend to be generated at the ends of the gate insulating film subjected to stresses during many manufacturing processes. This is considered to be the reason why breakdown is likely to occur at the ends.

According to the antifuse element 300 of the present embodiment, because the end 111 of the gate electrode 110 is formed in a zigzag configuration, it is longer than the linear one. Breakdown is thus likely to occur at the zigzag-shaped end. When the end is subjected to breakdown, the distance of the current path through the channel region 120 becomes substantially zero.

Therefore, according to the present embodiment, variation in resistance after breakdown is further suppressed and the resistance after breakdown is further reduced.

FIGS. 8A and 8B show a configuration of main parts of an antifuse element 400 according to a fourth embodiment of the present invention, where FIG. 8A is a schematic plan view and FIG. 8B is a schematic cross-sectional view along the line F-F shown in FIG. 8A. Elements including contacts are omitted in the drawings.

According to the antifuse element 400 shown in FIGS. 8A and 8B, a gate electrode 410 is formed in a U-shaped configuration. Parts of a first part 411 and a second part 412 are placed on the active region 102. Other part of the gate electrode 410 is placed on the element isolation region 108. The depletion channel region 120 is formed at the part of the active region 102 covered by the gate electrode 410 and the gate insulating film 130. The diffusion layer region 122 is formed at the other part of the active region 102.

As shown in FIGS. 8A and 8B, the first part 411 and the second part 412 of the gate electrode 410 are positioned along the X direction. Accordingly, even if the relative position with respect to the active region 102 is slightly shifted in the X direction during patterning of the gate electrode 410, at least one of the first and second parts 411 and 412 is formed so as to cover the active region 102. That is, even if a channel length L is set to be extremely short, overlapping of the gate electrode 410 on the active region 102 is surely maintained. In the fourth embodiment, because the channel length L can be set to be extremely short, the resistance of the channel region 120 can be kept extremely low.

FIG. 9 shows a configuration of main parts of an antifuse element 500 according to a fifth embodiment of the present invention. Because schematic cross-sectional views along the lines G1-G1 and G2-G2 shown in FIG. 9 are the same as FIG. 8B, they will be omitted.

According to the antifuse element 500 shown in FIG. 9, a gate electrode 510 is formed in an O-shaped configuration. Parts of a first part 511 to a fourth part 514 are placed on the active region 102. The other part of the gate electrode 510 is positioned on the element isolation region 108. The depletion channel region 120 is formed at the part of the active region 102 covered by the gate electrode 510 and gate insulating film 130 (see FIG. 8B). The diffusion layer region 122 is formed at the other part of the active region 102.

As shown in FIG. 9, the first part 511 and the second part 512 of the gate electrode 510 are positioned along the X direction. Meanwhile, the third part 513 and the fourth part 514 of the gate electrode 510 are positioned along the Y direction. Therefore, even if the relative position with respect to the active region 102 is slightly shifted during patterning of the gate electrode 510, at least one of the first to fourth parts 511 to 514 is formed so as to cover the active region 102. Even if the channel length L is set to be extremely short, overlapping of the gate electrode 510 on the active region 102 is surely maintained. Like in the fourth embodiment, because the channel length L can be set to be extremely short, the resistance of the channel region 120 can be kept extremely low.

The present invention is in no way limited to the aforementioned embodiments, but rather various modifications are possible within the scope of the invention as recited in the claims, and naturally these modifications are included within the scope of the invention.

For example, while the end 111 of the gate electrode 110 is formed in a zigzag configuration in the antifuse element 300 of the third embodiment, the method for extending the end of the gate electrode is not limited to such a configuration and any non-linear configurations will suffice. Considering that as the end of the gate electrode becomes longer, breakdown is likely to occur in the vicinity of the end, configurations that realize an effectively long distance of the unit interval like the zigzag configuration are preferably used.

Variations of the configuration of the gate electrode 110 whose end is formed in a non-linear configuration are shown in FIGS. 10A to 10D. In the present invention, such variations all correspond to “the zigzag configuration”. The planar configuration of the gate electrode does not coincide perfectly with the pattern on a reticle and patterns with some rounded off corners are provided. Such patterns with rounded off corners are included in the zigzag configuration. 

1. A semiconductor device having an antifuse element, the antifuse element comprising: a first semiconductor region of a first conductivity type; a diffusion region of a second conductivity type formed in the first semiconductor region, the diffusion region being electrically connected to a first electrode via a contact electrode, the diffusion region having a predetermined edge of non-linear shaped so as to form a concave portion; a second semiconductor region of the second conductivity type electrically connected to the diffusion region, the second semiconductor region and the diffusion region being in a conductive state, and the second semiconductor region being in contact with the predetermined edge of the diffusion region; an insulating film formed on the second semiconductor region; and a second electrode formed on the insulating film to cover the second semiconductor region, wherein the antifuse element can be programmed by a dielectric breakdown of the insulating film by applying a voltage between the second semiconductor region via the first electrode and the second electrode.
 2. The semiconductor device as claimed in claim 1, further comprising an element isolation region surrounding the antifuse element.
 3. The semiconductor device as claimed in claim 2, wherein the second electrode is elongated on the element isolation region so that a part of the second electrode covers the element isolation region.
 4. The semiconductor device as claimed in claim 2, wherein the element isolation region includes a predetermined portion closer to the second electrode than the diffusion region, an area between the predetermined portion of the element isolation region and the predetermined edge of the diffusion region is free from another diffusion region coupled to the first electrode independent from the diffusion region.
 5. The semiconductor device as claimed in claim 1, wherein the diffusion region has a substantially rectangular shape, the predetermined edge being one of edges of the rectangular shape.
 6. The semiconductor device as claimed in claim 1, wherein the second semiconductor region is smaller in area than the diffusion region.
 7. A semiconductor device having an antifuse element, the antifuse element comprising: a first semiconductor region of a first conductivity type; a diffusion region of a second conductivity type formed in the first semiconductor region, the diffusion region being electrically connected to a first electrode via a contact electrode; a second semiconductor region of the second conductivity type electrically connected to the diffusion region, the diffusion region and the second semiconductor region being arranged in a first direction; an insulating film formed on the second semiconductor region; and a second electrode formed on the insulating film, a first width of the second electrode in a second direction different from the first direction being narrower than a second width of the diffusion region between first and second edges thereof that crossing the second direction, wherein the antifuse element can be programmed by a dielectric breakdown of the insulating film by applying a voltage between the second semiconductor region via the first electrode and the second electrode.
 8. The semiconductor device as claimed in claim 7, further comprising an element isolation region surrounding the antifuse element.
 9. The semiconductor device as claimed in claim 8, wherein the second electrode is elongated on the element isolation region so that a part of the second electrode covers the element isolation region.
 10. The semiconductor device as claimed in claim 8, wherein the element isolation region includes a predetermined portion closer to the second electrode than the diffusion region, an area between the predetermined portion of the element isolation region and the predetermined edge of the diffusion region is free from another diffusion region coupled to the first electrode independent from the diffusion region.
 11. The semiconductor device as claimed in claim 7, wherein the diffusion region has a predetermined edge of non-linear shaped so as to form a concave portion, the second semiconductor region being arranged at the concave portion.
 12. The semiconductor device as claimed in claim 11, wherein the predetermined edge includes first and second portions extending in the first direction, the concave portion being arranged between the first and second portions.
 13. The semiconductor device as claimed in claim 7, wherein the second semiconductor region is smaller in area than the diffusion region.
 14. A. semiconductor device having an antifuse element, the antifuse element comprising: a first semiconductor region of a first conductivity type; a diffusion region of a second conductivity type formed in the first semiconductor region, the diffusion region being electrically connected to a first electrode via a contact electrode; a second semiconductor region of the second conductivity type electrically connected to the diffusion region, the second semiconductor being in contact with the diffusion region; an insulating film formed on the second semiconductor region; and a second electrode formed on the insulating film, the second electrode having an edge aligned with an edge of the insulating film, wherein the antifuse element can be programmed by a dielectric breakdown of the insulating film by applying a voltage between the second semiconductor region via the first electrode and the second electrode.
 15. The semiconductor device as claimed in claim 14, further comprising an element isolation region surrounding the antifuse element.
 16. The semiconductor device as claimed in claim 15, wherein the second electrode is elongated on the element isolation region so that a part of the second electrode covers the element isolation region.
 17. The semiconductor device as claimed in claim 15, wherein the element isolation region includes a predetermined portion closer to the second electrode than the diffusion region, an area between the predetermined portion of the element isolation region and the predetermined edge of the diffusion region is free from another diffusion region coupled to the first electrode independent from the diffusion region.
 18. The semiconductor device as claimed in claim 14, wherein the diffusion region has a predetermined edge of non-linear shaped so as to form a concave portion, the second semiconductor region being arranged at the concave portion.
 19. The semiconductor device as claimed in claim 18, wherein the predetermined edge includes first and second portions extending in parallel, the concave portion being arranged between the first and second portions.
 20. The semiconductor device as claimed in claim 14, wherein the second semiconductor region is smaller in area than the diffusion region. 